The present invention is directed generally to vehicular liquid sprayers and, more particularly, to an improved automatic control system therefor.
The problems involved in maintaining a relatively uniform density of sprayed liquid from a liquid product vehicular sprayer have long been recognized. For example, in a vehicular liquid sprayer of the type having a spray bar system and a pump for pumping liquid product to the spray bar system it was initially the practice to manually preset either the pump speed or the spray bar pressure in accordance with settings indicated on a chart for a preselected spread density at a fixed vehicle speed, and to then operate the vehicle at that fixed speed. However, it is not always convenient or possible to maintain a precise vehicular speed during the spraying operation. Moreover, a number of other factors which affect the achieved spread density may vary from time to time during the spreading operation. For example, the nominal values of the density of the liquid being spread and the nozzle flow characteristics may vary over time, as may the pressure actually experienced at the nozzles at a given, nominally fixed pump speed.
It has heretofore been proposed, as disclosed in U.S. Patent to Wilder et al U.S. Pat. No. 3,344,993, to vary the speed of the product pump with the vehicle speed in accordance with the ratio between the speed of the product pump and vehicle speed required to maintain a desired density of spread. In Oligschlaeger U.S. Pat. No. 3,877,645, it was further proposed to solve problems associated with the Wilder et al arrangement by controlling a valve to vary the flow rate of liquid product, rather than the pump speed, in accordance with the required ratio between vehicle speed and the pressure of the liquid at the nozzles to achieve the desired application rate.
The foregoing systems were further improved upon in Steffen U.S. Pat. No. 4,052,003, wherein operator accessible programmable controls were proposed. These controls were arranged to vary the control signal fed to a control valve interposed between the pump and the nozzles in accordance with liquid spraying parameters such as the nominal nozzle flow characteristics, the number of nozzles and the spacing between nozzles, and in accordance with the desired application rate. These improvements eliminated the necessity in the prior systems of referring to tables in order to set the proper ground speed to pressure ratio for maintaining a desired application rate, taking into account these other factors.
While each of the foregoing systems has found widespread acceptance, there is room for yet further improvement. For example, it is desirable to avoid "hunting" in the operation of the flow control valve in response to changes in the required pressure for maintaining a desired application rate. Further in this regard, it is desirable to maintain relatively smooth operation of the flow control valve in achieving corrections or variations in the pressure to maintain the desired application rate.
Moreover, it is known that the inertia of the control valve and the lag in the motor utilized to drive the control valve tend to cause delays in achieving a desired pressure in response to the control signal applied to the motor. Hence, it is desirable to adjust the control signal to overcome these factors so as to achieve a more responsive operation of the control valve. On the other hand, below a given minimum pressure, the nozzles will not deliver the desired spray pattern. Hence, the control system should close the valve at or below this pressure.
Additionally, it is known that liquid product density and nozzle flow characteristics often vary in practice from their nominal values. Accordingly, it is desirable to provide corresponding corrections in the response of the control system to correct for these variations. In this regard, the relative density of a given supply of liquid may vary from the nominal density of that liquid. Similarly, the nominal flow characteristics of a given nozzle often vary due to wear of the nozzle over a period of use.